Thinking Inside the Box (Culvert): Developing a Low-Cost, Easy-to-Install Retrofit Prototype for Fish Passage

This project addresses a need to develop a low-cost, easy-to-install, and safe culvert retrofit for fish passage. Culverts can create barriers to fish movement due to fast-flowing water with no resting areas, shallow flow, and/or lack of cover. While new culvert design guidance addresses these concerns, many existing culverts have known fish passage issues that are not slated for replacement. We previously investigated a potential solution, using mussel spat rope, a fibrous plastic rope that has been demonstrated to facilitate fish passage in New Zealand. This design showed promise in laboratory, fish, and field trials. However, despite interest, concerns over the release of plastic into the environment have inhibited its use. Therefore, we leveraged this experience to investigate new solutions with benefits similar to the installation of mussel spat rope (i.e., low-flow resting areas, cover, and minimal impact to culvert capacity) but that are made with bio-based sustainable materials. The goals of this project were to 1) identify appropriate materials and 2) design and test protypes in flume experiments. We have several viable prototype designs ready for field-scale testing and/or deployment made with a range of non-plastic materials.